Magnetic storage media having pre-written servo patterns are often used for storage and retrieval of data. Magnetic tape is an economical medium for storing large amounts of data, and pre-recorded servo patterns interspersed with data tracks enable higher data storage density on the tape. Magnetic tape cartridges are often used to back up large amounts of data at large computing centers. Magnetic tape cartridges also have applications in the backup of data stored on smaller computers such as personal computers.
Servo patterns are often prerecorded and verified during the tape manufacturing process. In this fashion, the servo patterns are recorded in the tape media prior to the media being used for data storage. Verification is often done by reading the servo pattern with a set of relatively narrow readers that are approximately the same width as the readers used in a tape drive. This method results in only a small fraction of the width of each of the servo bands being verified. As such, servo pattern defects that cover only a small portion of the width of the servo band may go undetected.
In an alternative verification method, a “full width” reader may be used to read the entire width of the servo band. In such a method, amplitude can be measured in an attempt to detect a defect that covers a portion of the width of the servo band. While this method does allow scanning of the full width of the servo band, this method is limited in its ability to detect narrow servo defects due to typical amplitude variation inherent in servo patterns. Furthermore, the unusually large width of the reader may preclude demodulation of the servo pattern and evaluation of many quality metrics which could detect narrow defects.
Verification of servo patterns may prevent tape cartridges with errors from being shipped to the customer. Servo pattern errors can cause permanent data errors when the customer attempts to use the defective cartridge for data storage and subsequent retrieval.